Every day i use my workstation, there i could use Hugo, produce content, build pages, upload them.
Every day i ly on my couch or sit in my shower writing some content with the tablet.
Sometimes i sit with my mobile in the forest behind the house.
Means: I need a solution online with some admin-tools to add/edit/delete content from everywhere with every medium.
How can i do that, please?
Damn what a poem! 
Google “git-based CMS” or use GitHub
With a database based Content Management System. Not with a STATIC site generator.
Have a look at forestry.io and Netlify CMS to find systems that put an interface on top of your Git repo to add/edit content. Both are free if you are the only user, but both have some issues with an existing setup (upload of images for instance does not work with page bundles in both systems).
Bad idea. Electronics and water. They just don’t mix well.
On more a serious note, you may want to check out the following recommendations:
If you’re in the Apple ecosystem, you might give Working Copy a try on iOS.